...or at least, the end of any simple theory regarding the extinction of our saurian predecessors. A few announcements from the annual meeting of the Geological Society of America last week concerned the simplicity of mass extinctions. For instance, new evidence suggests the Chicxulub meteor impact was not the sole cause of the end-cretaceous extinction:
The Chicxulub impact may, in fact, have been the lesser and earlier of a series of meteors and volcanic eruptions that pounded life on Earth for more than 500,000 years, say Princeton University paleontologist Gerta Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany. A final, much larger and still unidentified impact 65.5 million years ago appears to have been the last straw, exterminating two thirds of all species in one of the largest mass extinction events in the history of life. It's that impact - not Chicxulub - which left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles.
Long before the sky started falling, dinosaurs felt the heat of global warming:
The story that seems to be taking shape is that Chicxulub, though violent, actually conspired with the prolonged and gigantic eruptions of the Deccan Flood Basalts in India, as well as with climate change, to nudge species towards the brink. They were then shoved over with a second large impact.
The Deccan volcanism did the nudging by releasing vast amount of greenhouse gases into the atmosphere over a period of more than a million years leading up to the mass extinction. By the time Chicxulub struck, the oceans were already 3-4 degrees warmer, even at the bottom, she says.
"On land it must have been 7-8 degrees warmer," says Keller. "This greenhouse warming is well documented. The temperature rise was rapid, over about 20,000 years, and it stayed warm for about 100,000 years, then cooled back to normal well before the mass extinction."
Marine species at the time suffered from the heat. Most adapted to the stress conditions by dwarfing, growing less than half their normal size and reproducing rapidly with many offspring to increase the chances for survival. The Chicxulub impact coincided with this time. By the time climate cooled back to normal, most tropical species were on the brink of extinction. Then the second large impact hit and pushed them over the brink - many straight to extinction.
Another theory, presented at the GSA meeting, may change the way we look at mass extinctions, all together. Paleontologists from Hobart and Williams Colleges, Ian West and Nathan Crystal Arens suggested mass extinctions are not caused by sudden meteoric impacts or the slow choking by an atmosphere filled with volcanic ash, but the rare times when the two types of events occur simultaneously:
Using databases that chart genera of marine organisms and their extinctions through the fossil record, West and Arens divided the last 488 million years of geologic history into four groups: times of suspected impact events (Pulses), times of massive volcanic eruptions (Presses), times when neither Presses nor Pulses occurred, and times when Press and Pulse coincided. They compared average extinction rates in geologic stages in each of these groups.
During stages when only impacts occurred, an average of 7.3% of genera became extinct every million years; 8.3% of genera became extinct in stages characterized by flood volcanism alone. When neither Press nor Pulse were active, 8.2% of genera became extinct. These averages are statistically indistinguishable. "Statistically speaking, extinction rates are not significantly higher at times of impact or volcanism vs. no geologic events," West said.
In contrast, when Press and Pulse events coincided, an average of 12.8% of genera became extinct per million years, statistically higher than the rate observed during other geologic stages.
Their model, called Press/Pulse theory, seems to fit intuitively well with Stephen Jay Gould's definition of punctuated equilibrium. More than that, it rings true with complexity theory. Simple impacts on an ecosystem lead to adaptation and diversity--complexity. Complex impacts, on the other hand, from various causes, lead to death--simplicity.
Are humans, harbingers of complexity, exempt from the rule? Ares and West suggest we are not. While we aren't suffering from worldwide volcanic eruptions, or constant bombardments from space,* we've altered the environment greatly, through agriculture and industrialization:
"We sought to rephrase the question," said Arens. "In the modern world, species are commonly endangered by some stress before the final death blow falls. It seems likely that biological systems in the past worked in similar ways. By demonstrating that the coincidence of long-term stress and catastrophic disturbance is needed to produce big extinctions, we hope to break down some of the polarization characteristic of many discussions of extinction. We hope to send people back to the data with a more inclusive hypothesis to test."
(*-I did see a rather bright meteorite flying due west over the Rockies, about an hour ago.)
Of course, I wonder if it might not be the environment that gets us, in the end. Complexity can suffocate in other ways. In this tech-happy, digital day our government thrives on piles of complex paperwork, rules, and regulations. This reminded me of a comment I saw recently (thanks Tristan!) in reference to an argument with airport security over a half-filled tube of toothpaste:
As Dee Hock, the founder of Visa and proponent of chaos theory and adaptability observes, simple rules lead to complex, rich behavior. Complex rules lead to stupid behavior.
At this rate, there's a substantial risk that air travel rules will evolve to become as complicated as tax laws, to the point where no one knows what's allowed, what isn't, or what to screen for.
So, if environmental upheaval and climate change can cause mass extinction, then what happens when you add red tape in the mix?
Red-tape largely exists, as I see it to manage fairness and safety over large populations. Any reasonably wise person can decide what is fair in a conflict between 2-3 people, regulation and laws are needed when we get in the thousands and millions. (It may not work well, but it does work to some degree)
If a large percentage of the population is suddenly eliminated, I would expect the amount of red tape we deal with to go down as dramatically. No one goes through airport security when airports no longer exist. Thus, in the face of a catastrophic event like a meteor impact, humans would adapt quickly.
However, perhaps slow climate change could be out undoing. If you throw a frog in a boiling pot, he'll jump right out. If you you put the frog in cool water and slowly bring it to a boil, the frog will unknowingly, calmly await his death.
Don't get me wrong, I'm not advocating some anarchistic society which exists without any sort of regulation. I just think the processes we already have are becoming less useful as they become more complex. When we can store information digitally, and process it fairly automatically with computers, then why involve mass amounts of paperwork for any civic pursuit?
I might just be temporarily jaded... I spent a good bit of time last week filling out forms to become a tutor at the community college. After the 50th page or so of security checks and tax forms, my good feeling about helping others began to wane.
Then again, I don't think I'm alone in my frustration. How easily can we adapt when we're spending most of our time on the official (and redundant) minutiae?
This was a very good blog. Its been becoming increasingly obvious for some time the the C-T extinction didn't add up. We always had the paleontologists fighting with with the impact theory people "but the fossil record was in gradual decline already". Its about time that the camps stop fighting for their favorite cause, and realize that these are complex historical events, which usually have multiple causes, some more important than others.